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Wednesday, September 19, 2012

Calorie restriction for longevity ~ For mice, not man

Work
in any field long enough and you get a “nose” for the job. It is an instinctive
reaction to some new event or idea, built on decades of the passive
accumulation of knowledge in ones chosen field. I’ve acquired such a nose an
did so quite early on. Instinctively, I could spot a good, original and
potentially new area of interest among a forest of dross. Equally, I could
sniff a no-hoper, a line of research rapidly going nowhere. I first heard a
lecture on calorie restriction over 15 years ago, appropriately at a hotel
affiliated to the Orlando Disney Park. Rats, whose energy intake was restricted
to 15 - 25% of caloric intake, lived longer than rats given as much as they
liked to eat of standard rat chow. I neither like nor dislike rats but it
remains that I really have no feelings for them of any substance. The fact that
the caloric restriction made them live longer was really of no interest to me,
other than to wonder how rats feel about longevity in a captive and restricted,
if not slave-like existence. However, translating this to humans really made me
titter. We live in an extraordinarily obesogenic environment with overweight
and obesity abounding and growing in prevalence to every corner of the globe
and with quack diets and trash books for every desirable attribute, including
weight loss and aging, dominating the mass media. So, it appears from the rat
handlers, thatwe are to think
about adding caloric restriction as an additional string to our public health
nutrition bow to beat the grim reaper and steal a few more mortal years. As one
of my teachers used to say in exasperation in class at daft responses: “Ye gods
and little fishes.”

The
effect of caloric restriction on longevity was first reported in 1935 and has
now been studied in yeast, worms, flies and rodents and a 15-15% restriction in
energy intake in the latter can increase longevity by up to 60%. Such is the
wealth of data on thesediverse
species that one must accept the literature that caloric restriction prolongs
life expectancy. The big question is the translation of that concept to man.
Relative to these species, we mature far more slowly and have a longer life
span. People often talk about human equivalents of “dog years” but in absolute
terms, we outlive dogs by at least 8 fold.

The
Calorie Restriction Society[1]
boasts 7,000 members. One such member is described in a journalistic piece on
the web site. This member is 48 years old, is fit as a fiddle, weighs 118
pounds which is 7 pounds less than the minimum recommended for his height, he
confines his energy intake to 1,500 calories a day and although his energy
expenditure is not described, he would appear to be very physically active. He
first got interested in caloric restriction as a tool to longevity when he was
faced with his first manifestation of aging, a receding hairline. Poor guy!!!

The
whole are of calorie restriction took a hit recently when the National
Institute on Aging published its long term study of energy restriction on
longevity in rhesus monkeys, a species far closer to man than yeast, flies,
worms and mice[2].A 20 year study examined the
effects of caloric restriction introduced to rhesus monkeys at varying stages
of life. No statistically significant differences were observed between control
monkeys fed ad libitum and those calorie-restricted (10-40% restriction). The
latter did achieve a longer life span than would normally be expected for this
species but the authors point out that they lived a privileged life of good
husbandry and veterinary care. The main causes of death did not differ between
the two groups:cancer, cardiovascular disease and general organ deterioration.
However, generally recognised beneficial biomarkers of health increased in the
caloric restricted monkeys but this did not translate into a longer life. In
fairness to the literature, another colony of monkeys elsewhere (different
diet, management and breeds)did
respond but in the world of science, it only takes one black swan to demolish a
theory. The recent Nature paper is that black swan.

From
a practical point of view, I can see a few dedicated enthusiasts sharing the
necessary skills via social networks to achieve successful caloric restriction
but I fail to see how it would be dealt with the great majority of the people.
Leaving aside the ever-present obesogenic food supply, how is the average
person to know exactly what their energy requirements are and then how to pare
that down by 20% or more of that to achieve the required level of calorie
restriction? How, especially with increasing age, do we ensure that caloric
restriction does not drift into malnutrition which in the older population is
so strongly associated with increased admission to hospitals, increased
complications hen there, longer stays and more frequent re-admissions.
Professor James Hill of the University of Colorado in his excellent book “The
Step Diet” [3],
recommends 25,000 steps per day plus rejection of 25% of the food served at
every meal, just to maintain weight loss. For the many fatties among us, moi
included, there is (a) the need to shed pounds to an appropriate avoirdupois a
la James Hill and (b) having done so, to then hit a 25% calories restriction.

It
ain’t going to happen. My nose was right!

Finally, apologies for the late post of this
blog but that happens. Also next two mondays are in Asia and a lot of teaching
at China Agricultural University in Beijing and Honk Kong University so I’ ll
try but please be understanding!

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"Ever seen a fat fox ~ Human obesity explored"

About Me

I graduated from University College Dublin in 1971 with an Masters in Agricultural Chemistry, took a PhD at Sydney University in 1976 and joined the University of Southampton Medical School as a lecturer in human nutrition in 1977. In 1984 I returned to Ireland to take up a post at the Department of Clinical Medicine Trinity College Dublin and was appointed as professor of human nutrition. In 2006 I left Trinity and moved to University College Dublin as Director of the UCD Institute of Food and Health. I am a former President of the Nutrition Society and I've served on several EU and UN committees on nutrition and Health. I have published over 350+ peer reviewed scientific papers in Public Health Nutrition and Molecular Nutrition and am principal investigator on several national and EU projects (www.ucd.ie/jingo; www.food4me.org). My popular books are "Something to chew on ~ challenging controversies in human nutrition" and "Ever seen a fat fox: human obesity explored"